This invention relates to a microwave enhanced CVD system under magnetic field, more particularly to an ECR (Electron Cyclotron Resonance) CVD (Chemical Vapor Deposition) system.
In the field of thin film formation techniques, there is a known photo enhanced chemical vapor deposition which is advantageous, compared with conventional CVDs such as a thermal CVD, or plasma enhanced CVD, in that a deposition can be carried out at relatively low temperature without injuring the surface on which a layer should be formed. The photo enhanced CVD has a further advantage of "wandering on a surface". Namely, atoms or molecules of the deposited layer preserve their active energy after being deposited on a surface of a substrate, and due to the active energy they move and also form a layer on a surface on which no deposition is carried out, thereby on an uneven surface is established a layer formation with an improved step coverage by CVD.
The photo CVD, however, is far short of carrying out deposition of a layer at high speed which is required from the commercial interest. It has therefore been desired to increase the deposition speed by a factor of tens.
On the other hand, a plasma CVD is known which utilizes glow discharge by means of high frequency or DC power supply to make a process gas plasma. This technique is advantageous in capability of relatively low temperature deposition. Especially, when an amorphous silicon layer is to be deposited, doping of hydrogen or halogen can be simultaneously carried out in order to neutralize recombination centers on the layer so that p-i-n or p-n junctions are easily obtained with improved characteristics. Such a plasma CVD also sufficiently copes with the demands of fast deposition.
Further, a CVD with Electron Cyclotron Resonance (ECR) has been known according to which a thick layer of 5000 .ANG. to 10 microns in thickness can be deposited at 10 .ANG. to 100 .ANG. per second. However, a reactant gas moves in parallel to the surface of a substrate making it impossible to form a layer on a depression such as a trench. In addition to this, argon atoms resonate at 2.46 GHz which requires a strong magnetic field of 875 Gauss, therefore requiring a very large coreless coil. As a result, due to the limited space available for exciting gas, a standard of fluctuation of 10% in thickness might be compromised even on a 3 inch disc wafer.